The present invention relates to an apparatus for producing ozone on a commercial scale and more precisely to high frequency tubular ozonizers. The invention can find application whenever production of large quantities of ozone are required, that is as much as hundreds of kilograms or even several tons of ozone per hour or more.
At present, ozone has a very wide range of application, which continues to expand extremely rapidly. Ozone applications range from the function of "pure" oxidizer in the perfumery and pharmaceutical industries to a bleaching and disinfecting agent in the food industry, and to non-ferrous and rare metals hydrometallurgy, where it is used as an intensive oxidizer for separating different metals. Ozone is used for the purpose of purification and disinfection of potable water in municipal water supply systems and for purification of industrial effluents (especially phenol contaminated effluents); ozone is also used in various branches of the chemical industry, for example, in hydrocarbon oxidation, production of synthetic fibers and production of most valuable vat dyes; in petrochemistry, and, as a very active oxidizer for bromide recovery from drilling water, in the production of pure chemical reagents, and many other materials.
In the paper and textile industries, ozone is used as a bleaching agent, as an oxidizer in neutralization processes of waste gases in various industrial production processes involving H.sub.2 S, SO.sub.2, NO and NO.sub.2, organic compounds vapors, etc., and it can also be used for oxidizing and neutralization of waste gases of thermal power stations, magnetohydrodynamic generators, etc.
Many of these processes require large quantities of ozone (tens and hundreds of kilograms of ozone per hour, or tons of ozone per hour) and, therefore, can be implemented only in the event that high capacity compact ozonizers which can deliver such quantities of ozone are available.
There are many designs for ozonizers known in the art. However, none of them can meet the requirements of modern technological processes which demand tons of ozone.
For example, there is known in the art a design for a multi-tube ozonizer which has a cylindrical housing with semi-spherical covers provided on the ends of the housing.
A tubular grid arranged inside the housing is cooled from the outside with water circulating in the intertubular space. Each tube of the tubular grid is a low voltage grounded electrode connected to the housing. Inside each such tube there is provided a high voltage electrode which is in the form of a pipe having a varying cross-section with a core disposed in the central expanded portion thereof to increase the linear velocity of the gas flow which is intended to cool the high voltage electrode.
The opposite surfaces of the high voltage and the low voltage electrodes are coated with a dielectric which acts as a dielectric barrier determining the specific "silent" discharge in the ozonizer. The narrowed ends of the high voltage electrodes extending from the tubular grid are fitted into one of two boxes which serve as an air distributor and an air collector, respectively, the air being fed to one box and led off from the other box via tubes connected to the housing of the ozonizer. The boxes are made of an insulating material, which feature, together with the cooling gas, which also possesses insulating properties, and which is passed through the boxes and the high voltage electrodes, permits the high voltage electrodes to be electrically insulated from the ozonizer housing and from the low voltage electrodes.
The gas to be ozonized is fed through a pipe under the semi-spherical cover of the housing and then passes in parallel flows through all ozonizing elements between the low voltage grounded electrodes and the high voltage electrode; then the ozonized gas, which has passed through the ozonizing elements, is collected under the second semi-spherical cover of the housing and thereafter is removed from the ozonizer through the discharge pipe.
Such an ozonizer is capable of working at a frequency of electric current of up to 150-200 Hz. However, at still higher frequencies the high voltage electrodes, which are cooled as mentioned above by a stream of air, become overheated and thus become inoperative.
Also known in the art are low-frequency ozonizers which have a housing with two semi-spherical covers, a tubular grid inside the housing made of stainless steel tubes which have diameters ranging from score of centimeters to 1.5-2 meters, and which is 1.5 to 3 m long, depending on the type and size of the ozonizer. Each tube of the tubular grid, cooled from the exterior side with direct flow of water contained in the intertube space of the ozonizer housing, acts as a low voltage electrode connected to the housing and grounded. A glass tube of somewhat smaller diameter is inserted into each tube, the glass tube being sealed at one end and coated from the inside with a current-conducting coating. Current from the high voltage side of a transformer is fed to this current-conducting coating inside the tube, the outer surface of the glass tube thus acting as a high voltage electrode. No special means are provided for cooling the high voltage electrode and hence for cooling the dielectric barrier. The cooling effect can be obtained only by the flow of ozonized gas.
In other types of known low voltage ozonizers, the operating principle of which is the same as the above-described ozonizers, the other end of the glass tube of the high voltage electrode is also sealed, with high voltage being fed through this other sealed end to the current-conducting coating applied to the inner surface of the glass tube. Here again no special means for cooling the high voltage electrode are provided and the cooling effect can be obtained only by the flow of ozonized gas.
Both these types of ozonizers, as well as many types which are similar to the above-described ozonizers in design, are intended for operation at current frequency of 50-60-80 Hz, although under the conditions of heavy-rate operation they can work at 200 Hz.
The above-mentioned ozonizers are of a relatively simple design and do not require any electrical conversion and supply means except common controlling and step-up transformers rated at 10 to 20 kilovolts. Due to the absence of special cooling for the high voltage electrode in these ozonizers, the concentration of the produced ozone is very low, being 3-5 grams of ozone per cubic meter of ozonized air, and the rate of power consumption is high. When producing ozone from air, the power consumption per 1 kg of ozone produced totals 18-30 kW-hr per kg of O.sub.3 at the above-mentioned concentrations and the power consumption increases sharply when a further increase of concentration of the produced ozone is required. In addition, a rapid increase of electric power consumption and reduction of ozone synthesis efficiency results from the increase of supply of current frequency in these ozonizers.
For example, with current frequency increasing from 50 to 200 Hz and a corresponding four-fold increase of the discharge power, the low frequency ozonizer efficiency increases from 2.5 kg/hr ro 6.5 kg/hr, becoming only 2.6 times as high, whereas the power consumption per kg of ozone produced increases in the ratio of 4 to 2.6, that is, 1.54 times. At increased frequencies the glass dielectric tends to become heated, resulting in dielectric break-down and thus in failure of the ozonizing element.
Also known in the art are plate-type ozonizers capable of operating at increased current frequencies of 400 to 500 Hz, which have a liquid cooling system for both the low voltage and high voltage electrodes. However, their design is rather sophisticated and, in addition, these ozonizers do not ensure even distribution of the cooling fluid over all cooled surfaces and even distribution of the flow of the ozonized gas in the reaction zone, this resulting in low concentration of ozone produced and high consumption of power for production of 1 kg of ozone per hour.
Also known in the art are tubular ozonizers capable of operation at increased current frequencies and embodying a system of tubular ozonizing elements connected in parallel. Each ozonizing element comprises a glass tube inserted and packed into a metal tubular grid and cooled from the outside by water contained in the ozonizer housing. This glass tube which is cooled by water from the outside acts as a low voltage electrode. A non-cooled metal high voltage electrode made of stainless steel is coaxially arranged inside the glass tube.
Owing to such design modification the unit is capable of operating at a current frequency of up to 500 Hz at voltages not higher than 7000-8000 volts, since water cooling of the glass dielectric considerably reduces the danger of its thermal break-down.
The following disadvantages are common in such ozonizers. The design and manufacture is complex mainly because of the difficulties experienced in securing and packing the glass tubes in the tubular grid. Owing to the complex design and the necessity of packing the glass tubes in the metal tubular grid, the length of the ozonizing elements is only about 300 mm and the total number of ozonizing elements in the largest ozonizers of this type is only 30. Owing to the high temperature of the gas in the discharge zone resulting from the fact that the high voltage electrode is not cooled (though being manufactured of stainless steel it easily withstands elevated temperatures of about 200.degree.-300.degree. C), the concentration of ozone produced is quite low, i.e. on the order of from 1.5 to 3.0 gr/cubic meter. Due to the elevated gas temperature in the discharge zone, the power consumption for the production of 1 kg of ozone is quite high. At a frequency of 500 Hz, power consumption is 30 kW-hr per kg of O.sub.3. Finally, in the case of a break-down or a rupture of a glass tube, the whole space of the discharge zone, as well as the piping which is normally occupied by the ozonizing gas, becomes filled with water.
Also known in the art are ozonizers made of glass and which are capable of operating at a current frequency of up to 10,000 Hz, both electrodes, that is, the low voltage electrode and the high voltage electrode, also being made of glass. The low voltage electrode is adapted to be cooled from the outside with water circulating in the common casing or housing, whereas the high voltage electrode is cooled from the inside with water obtained from an insulated source. Due to the fact that both electrodes are cooled with flowing water, (although the flow is not too intensive) the electrodes being at the same time dielectric barriers, the temperature conditions become less intensive and this permits the production of ozone at a concentration of about 8 gr per cubic meter with power consumption of about 20 kW-hr per kg of O.sub.3, based on the power supplied to the transformer, or about 28 kW-hr per kg of O.sub.3, based on the power supplied to the frequency converter.
A disadvantage of the ozonizers of such a design resides in their low mechanical strength which makes it difficult to use them for large ozonizing installations required by modern industry. In case even one electrode breaks down or fails, all gas lines become filled with water, thus instantly causing the unit to stop operation.
Despite the fact that both electrodes are cooled with flowing water, the cooling is not as sufficiently intensive as needed when using such high frequency current as 10000 Hz, thus all the positive effect which could be achieved by operating at a frequency of 10000 Hz cannot be, in fact, achieved.
The most similar design in comparison to the disclosed ozonizer is the ozonizer of U.S. Pat. No. 3,766,051 which is capable of operating at frequencies of up to 5000 Hz.
The patented ozonizer referred to embodies a system of ozonizing elements, each consisting of two concentric tubes, one made of metal and the other of a dielectric material (for example, glass) coated with a metal. The high voltage electrode is cooled with water which occupies the common casing or housing of the ozonizer and the space between the ozonizing elements.
The silicone oil, which cools all the high voltage electrodes of the ozonizer, is distributed among the electrodes by means of two manifolds which form the end faces of the ozonizer.
In the described ozonizer, the thin-walled tubes made of a dielectric (glass in particular) are used in the construction as supporting and mechanically stressed parts. These tubes when used as both the low voltage electrodes and the high voltage electrodes should be fixed in the tubular grid and, consequently, in addition to the mechanical stress of the tubular grid and their own weight, they should also bear the weight of the cooling liquid which circulates in the electrodes.
In addition, the sealings and fastenings of these dielectric tubes (FIG. 3, numeral 12) in the tubular grid should be made tight to prevent penetration of water or other cooling liquid into the discharge zone. The above patent gives no explanation at all as to how the thin-walled dielectric tubes (in particular those made of glass) are sealed and secured in the tubular grid of the ozonizer; nor does it explain the manufacture of the design configuration of the high voltage electrodes with dielectric materials (particularly glass) or how these electrodes are connected to the manifold.
In addition, in the cooling system for the low voltage electrodes, water freely fills the vast intertubular space in the ozonizer housing and, hence, a sufficiently high heat transfer coefficient from the low voltage electrodes to the cooling liquid cannot be achieved. The cooling of the high voltage electrodes with silicone oil, which is a viscous cooling agent having low heat capacity and low heat conduction also makes it impossible to achieve high intensity cooling of the high voltage or the low voltage electrodes. This disadvantage of the cooling system prevents the use of the advantages offered by a high frequency current. Thus, although a direct contact between the cooling liquid and the dielectric barriers does protect these barriers from a thermal electric break-down, nevertheless, the temperature conditions in the reaction zone of the ozonizer, when operating at higher frequencies, remain rather intensive and unfavorable to the synthesis of ozone.
Due to the low efficiency of the cooling system of the electrodes in the described ozonizer, the efficiency of its operation is rather moderate even when ozone is synthesized from oxygen. At frequencies of about 2000 Hz, with 1.5-1.6 weight % concentration of the produced ozone, power consumption for the synthesis of ozone in this ozonizer is 10.6 kW-hr per kg of ozone (4.8 kW-hr per pound) in the best of all published examples.
The patent discloses no clear description of the ozonizer elements which permit the high voltage electrodes to be coaxially aligned within the low voltage electrodes, especially in the case of a multi-element ozonizer, although it is pointed out therein that .+-.0.017 inch accuracy of alignment is attained (that is, .apprxeq. 0.4 mm).
Thus, it is seen that the technological parameters of available ozonizers fail to meet the requirements of modern industrial processes. The output of the largest available ozonizer does not exceed 10-12 kg, the weight of the unit per se being 5-6 tons. The power rating of such ozonizers is in the range of 200 kW.
The object of the invention is to provide a substantially more efficient and highly productive ozonizer, this object being achieved without increasing the dimensions of the ozonizer, the overall dimensions of the largest ozonizer unit know already exceeding 2-3 meters in diameter and 3-4 meters in length. Consequently, the task of producing quantities of ozone to be measured in tons of output must be solved by considerably increasing, at least twentyfold, the electric capacity and output without increasing the overall dimensions of the ozonizer per se.
It is, accordingly, an object of the present invention to provide a novel ozonizer construction permitting the output thereof to be increased 50 to 100 times, without reducing the output of ozone per energy unit and without substantially increasing the overall dimensions and the cost of installation thereof.
Another object of the invention is to provide a novel ozonizer construction capable of operation without failure at a power on the order of hundreds and thousands of kilowatts at current frequencies of 1000-20,000 Hz without overheating the ozonizing elements or reducing the efficiency of synthesis of ozone (power output).
Still another object of the invention is to provide a multielement ozonizer construction which permits each high voltage electrode to be coaxially aligned inside the low voltage electrode with an accuracy of 0.1 mm, such an accuracy being necessary to achieve efficient and economic operation.